There are known measuring devices including a base on which is mounted to pivot about a horizontal axis a first end of an articulated arm having a second end provided with a pointing member such as a feeler or a laser beam emitter. The second end of the arm is also provided with a manipulator handle that enables the operator to apply the feeler against the surface of the object to be measured or to direct the laser beam emitter toward a portion of the object to be measured.
The articulated arm generally comprises a first segment articulated on one side to the base and on the other to a second segment having a free end provided with an articulated wrist carrying the manipulator handle and the pointing member.
In these measuring devices, the articulated arm is generally designed to have a stable position of rest or non-use in which the first segment extends substantially vertically abutted against a portion of the base and the second segment is folded against the first segment. In this position, the centre of gravity of the assembly comprising the segments, wrist, manipulator handle and pointing member lies substantially in vertical alignment with the base and tends to maintain the first segment abutted against the base, thus ensuring the stability of said assembly.
However, an accidental impact on the arm risks causing it to leave its rest position, the arm then tilting because of the effect of its own weight, starting a downward movement until the arm strikes an obstacle. This type of impact can lead to deterioration of the pointing member and also of the members guiding movement of the arm and, more generally, of the structure of the arm as a whole.
It is known to mount an elastic cylinder between the base and the first segment of the arm to compensate the weight of the arm. An ancillary effect of this cylinder is to reinforce the stability of the arm in the rest position.
Although the risk of accidental tilting of the arm is then reduced, it nevertheless remains high.
To reduce this risk further, some measuring devices comprise a member for blocking sliding of the rod of the cylinder. This locking member takes the form of a removable spacer having a substantially U-shaped cross section that is engaged over the rod of the cylinder when the arm is in the rest position so that the spacer opposes movement toward each other of the body of the cylinder and the free end of the rod of the cylinder. There nevertheless exists a risk of losing the spacer, in which case the locking of the arm is no longer possible, or, to the contrary, of leaving the spacer on the rod when the operator exerts a force on the arm tending to cause it to leave its rest position, in which case the arm and the spacer are subject to stresses risking weakening or even deteriorating them.